Before you read the following did you uninstall the old drivers first? If not the the following advice may be useless because it could just be a crazy driver issue.
Go into the BIOS and make sure that y our RAM is set to the recommended speed, voltage, and timmings. First run memtest for an hour or so. If it passes then boot it up and run Prime 95. You should also be running everst or something while running prime to monitor your temps. If you get an error it could just be over heating so you would have to whipe off the old thermal paste and apply new paste. If you get an error but it's not getting too hot at stock clocks then you may want to try downclocking the RAM. Even if it passes memtest it may just not be suitable to run at its advertised speed, settings, and voltage so it may have problems under load. In that even increasing your memvoltage by .1v should take care of it if you don't want to go through the hassel of an RMA. You should also check the ASUS website to see if the motherboard has any problems with your particular RAM. You may just need a BIOS update.
If it's stable under prime with the latest BIOS but still crashes with games then it could be the PSU, GPU or the motherboard. Most likely culprit would be the PSU. If you monitor the voltages and notice great fluctuation then the PSU could be making your system unstable.